Process of manufacturing evoh/polyester bistretched film and the film thus obtained

ABSTRACT

A multilayer film is formed by coextruding and bistretching EVOH, binder and polyester followed by heat treating for less than 8 seconds at a temperature between 170° C. and 250° C.

FIELD OF THE INVENTION

The invention relates to a process of manufacturing a EVOH/Polyester(coextruded) bistretched film. The invention also relates to such afilm, showing high barrier properties and high mechanical properties.

BACKGROUND OF THE INVENTION

Extrusion of multilayer films is well-known. Stretching of films, beingmonolayer or multilayer films, is known as well.

The above techniques have been applied to many different types of films,in order to obtain the desired results. One multilayer film that wouldbe of high interest is a film containing a layer of EVOH and a layer ofpolyester. The layer of EVOH would impart barrier properties such as gasbarrier properties against oxygen, carbon dioxide, helium, aroma andflavors, etc. . . . The layer of polyester would impart mechanicalproperties, such as Young's modulus, tensile strength, heat resistance,clarity, etc. . . . Since these two types of polymers are notcompatible, a coextrusion binder is necessary. Thus, one would look forfilms having one layer of EVOH, one layer of coextrusion binder and onelayer of polyester.

The process of manufacturing such films is, however, very delicate.Especially, stretched films are very difficult to manufacture, since thelayer of EVOH is very difficult to stretch, especially to bistretch. Asa matter of fact, polyester, being nearly amorphous at the exit of theextruder, can be easily stretched, either simultaneously orsequentially, and high quality film is easily obtained. The EVOH layeron the contrary, has a high tendency to crystalise under heat andstress, so that a sequential stretching is not possible: stretching inMD direction forms a crystalline EVOH layer, that breaks whilst theattempt to stretch in TD direction. Simultaneous stretching is thusrequired. Eventually, the stretched films are heat set, so as to developthe mechanical properties of the film, thanks to the polyester layer.

Thus, there is a need for a method that would allow the production ofvaluable multilayer EVOH/PET films, but would also be cost effective andeasy to carry out.

JP-A-55139263 discloses a process where a multilayer film is bistretchedthen heat treated at a temperature below the melting point of the EVOHmaterial. This, however, is not satisfactory, since the melting point ofall EVOH grades suitable for high barrier applications is below 190° C.,preferably below 180° C., most preferably below 170° C. Such lowheat-set temperatures are not appropriate to maintain thethermo-mechanical strength of the outer polyester layers, resulting fromthe biaxial stretching. This would lead to a high thermal shrinkage andthe high mechanical strength of polyester film would be lost at highertemperatures.

JP-A-63272548 discloses a process for manufacturing a laminate stretchedfilm comprising coextruding a 5-layer film, especiallypolyester/binder/EVOH/binder/polyester, simultaneously bistretching it,and heat-treating it under the following conditions:

0.5≦X≦5

EVOH melting point+40° C.≦T≦polyester melting point 8 sec≦t≦25 sec

where:

X=total polyester thickness/EVOH thickness

T=heat treatment temperature

t=heat treatment time

Examples given in this document provide simultaneous bistretching at atemperature of 90° C., at ratios of 3.3×3.3, followed by heat treatmentat a temperature of about 230° C., for a duration of about 15 sec. Therespective polymers are PET, EVOH and modified PET or modified EVA resinas a binder. The thicknesses (unstretched/stretched) of the EVOH and PETlayers are respectively about 54 μm/5 μm and about 130 μm/12 μm, givinga X value of about 2.5. The EVOH melting point is about 180 (leading toon heatset temperature of 220° C. for EVOH mp+40° C.) while PET meltingpoint is about 260° C. At this high heatset temperatures, the filmstarts to crystallize and gets brittle very fast. Heatset times higherthan 8 seconds will definitely lead to film breakage in the oven and aloss of mechanical properties, especially elongation, due to highcrystallization and brittleness thereof. Additionally, running a filmline with such high hold-up times in the heatset zones would requireeither very long heatset zones in the oven or very low line speeds. Thisis economically not suitable for such a product.

SUMMARY OF THE INVENTION

The object of the present invention is a process where the heattreatment is carried out during a time below 8 sec., and at atemperature preferably below 220° C.

The resulting film shows enhanced properties, especially when the ratioof thicknesses of polyester to EVOH is higher than 5.

DETAILED DESCRIPTION OF THE INVENTION

The polyester used in the invention is any polyester where the majorpart of it is comprised of any aromatic repeating ester units. The termpolyester in this invention refers to a polymer that is obtained bycondensation polymerization of an aromatic dicarboxylic acid such asterephthalic acid or 2,6-naphthalene dicarboxylic acid and of analiphatic glycol such as ethylene glycol, 1,4-butanediol or1,4-cyclohexane dimethanol. These polymers, in addition to beinghomopolymers, may also be copolymers having a third component or severalcomponents. In this case, the dicarboxylic acid component may be, forexample, isophthalic acid, phthalic acid, terephthalic acid,2,6-naphthalene dicarboxylic acid, 4,4′-diphenyldicarboxylic acid,adipic acid, sebacic acid, decanedicarboxylic acid and 1,4-cyclohexanedicarboyxlic acid; the oxycarboxylic acid component can be, for example,p-oxybenzoic acid and the glycol component can be, for example, ethyleneglycol, diethylene glycol, triethylene glycol, propylene glycol,butanediol, neopentyl glycol, 1,4-cyclohexane dimethanol, polyethyleneglycol and polytetramethylene glycol.

Examples of such polyesters are polyethylenenaphthalate (PEN),polybutyleneterephthalate (PBT), polyethyleneterephthalate (PET), thelatter PET being the preferred polyester.

Mixtures are also possible, optionally with another polymer differentfrom a polyester. The intrinsic viscosity of the polyester that is usedin the invention may vary from e.g. 0.45 to e.g. 0.7, measured inphenoltetrachloreethane at 30° C. The MW may vary within broad limits,e.g. between 10000 to 30000 g/mol.

The binder material is any material that is adhesive and allow thepolyester and EVOH layers to show adhesion, with either adhesive ruptureor cohesive rupture. The skilled man will choose the binder thanks toits general knowledge or thanks to routine tests.

Examples of such binders include modified polyolefins, polyacrylates,polyurethanes, polyesters, etc.

Examples of binders are the following (co)polymers, grafted with maleicanhydride or glycidyl methacrylate, in which the grafting rate is forexample from 0.01 to 5% by weight:

PE, PP, copolymers of ethylene with propylene, butene, hexene, octene,butadiene, EPR, EPDM, containing, for example, 35 to 80% by weightethylene, as well as any styrene-based block copolymers such as SBS,SIS, SEBS, and the like;

ethylene and vinyl acetate (EVA) copolymers containing up to 40% byweight vinyl acetate;

ethylene and alkyl (meth)acrylate copolymers containing up to 40% byweight alkyl(meth)acrylate;

ethylene and vinyl acetate (EVA) and alkyl (meth)acrylate copolymers,containing up to 40% by weight comonomers.

Further examples of binders are the following (co)polymers, in whichethylene represents preferably at least 60% by weight and where thetermonomer represents, for example, 0.1 to 10% by weight of thecopolymer:

ethylene/alkyl (meth)acrylate or methacrylic acid/maleic anhydride orglycidyl methacrylate copolymers;

ethylene/vinyl acetate/maleic anhydride or iglycidyl methacrylatecopolymers;

ethylene/vinyl acetate/alkyl (meth)acrylate or methacrylic acid/maleicanhydride or glydicyl methacrylate copolymers. The term “alkyl(meth)acrylate” stands for C1 to C6 alkyl, such as methyl, ethyl, butyland 2-ethylhexyl methacrylates and acrylates. Moreover, thesepolyolefins can also be cross-linked using any suitable process or agent(di-epoxy diacid, peroxy, etc.)

Still further examples of binders include

grafted copolymers constituted by at least one monoamino oligomer ofpolyamide and of an alpha-mono-olefin (co)polymer grafted with a monomerable to react with the amino functions of said oligomer;

Mixtures thereof are also envisaged. The molecular weight of thesebinders can also vary greatly, as those skilled in the art willunderstand.

Examples of such binder compositions are provided in the followingpatents, this list not being exclusive:

FR-A-2,291,225, FR-A-2,132,780, EP-A-0,210,307, EP-A-0,033,220,EP-A-0,266,994, EP-A-0,171,777, EP-A-0,342,066, EP-A-0,218,665, U.S.Pat. No. -4,758,477, U.S. Pat. No. -4,762,890, U.S. Pat. No. -4,966,810,U.S. Pat. No. -4,452,942, U.S. Pat. No. -3,658,948, U.S. Pat. No.-5,217,812, all of which being incorporated herein by reference.

A prefered binder is an anhydride-modified ethylene vinyl acetatecopolymer.

The term “EVOH” as used in the instant invention aims at designingethylene/vinyl alcohol copolymers containing for example from 15 to 80,preferably 20 to 50 mol % of ethylene. A preferred EVOH contains morethan 30 mol %, especially more than 40 mol % of ethylene. This kind ofcopolymer is well-known in the art, and can be obtained, for example, bysaponification of an ethylene/vinyl acetate copolymer, with asaponification degree of generally more than 90%, most preferably morethan 95%. A third monomer can be present, in an amount not adverselyhindering the barrier porperties. It is permissible to blend othercomponents keeping within a range of not adversely hindering the barrierproperties. The blending component should preferably be not more than 40weight %, more preferably not more than 30 weight %, most particularlynot more than 20 weight %.

Such blending resins, for example, include the above ethylene-vinylalcohol copolymers having an ethylene content different from those whichare used as main components, or ethylene-vinyl alcohol copolymers havingan ethylene content greater than those which are used as maincomponents, or their partially saponified products, polyamide typepolymers, polyester type polymers, ethylene-vinyl ester copolymers,ethylene-aliphatic unsaturated aliphatic acid copolymers,ethylene-aliphatic unsaturated aliphatic acid ester copolymers, ionomerresins, styrene-conjugated diene block copolymers, a partiallyhydrogenated product of said block copolymer, or else these polymerswhich have been modified, for example, by grafting a monomer having acarboxylic acid group as a polar functional group, copolymers ofethylene and carbon monoxide, or additionally with the vinyl acetatecomponent or a resin wherein at least some of the acetate groups havebeen converted into hydroxyl groups, and ethylene, propylene resins, andthe like, other that those mentioned above; at least one from theseshould be used.

Various additives, such as UV-agents, stabilizers, sliding agents,antioxidants, fillers, etc. can be added to each component of the layer,in classical amounts.

The coextrusion referred to in the instant invention is any classicalextrusion. The extrusion may be of the type T-die, with feeding block,of the blow film type, etc. Also encompassed in the invention is theextrusion, where individual films are produced, which are then laminatedon each other so as to build up a raw multilayer film. In fact, anymethod that produces a raw film is appropriate; preferably this methodis coextrusion.

The extrusion temperature of the EVOH may optimized to reach highbarrier properties; said temperature may generally be lower than 220°C., preferably between about 180 and 210° C.

The biaxial stretching or bistretching is carried out simultaneously. Itincludes stretch ratios of 2 to 5, especially 2.5 to 4, in eachdirection. The ratio MD stretch ratio/TD stretch ratio is generallycomprised between 0.5 to 2, especially 0.7 to 1.3. The suitablestretching temperature is comprised between 75 and 130° C., generallyabout 90° C. The raw film to e stretched can be preheated, if necessary.Preheat temperature can be as high as the stretching temperature; forexample preheat can be performed at a temperature of 80° C. (for about10 sec) while stretching is carried out at a temperature of 90° C. Anysimultaneous stretching apparatus can be used; preferably polyesterstretching apparatuses are used. Examples of simultaneous bistretchingapparatus are disclosed in the following US patents, all incorporatedherein by reference: U.S. Pat. Nos. 4,675,582; 4,825,111; 4,853,602;4,922,142; 5,036,262; 5,051,225; 5,072,493 and 5,416,959.

The heat treatment (or heatsetting) referred to in the instant inventionis the classical heat treatment carried out for polyesters; classicalapparatuses are used like introducing hot air or using infrared lamps,etc. Either “heatset” or “heat treatment” is used in the instantinvention, without any distinction.

The raw film shows a total thickness generally between about 10 and 1000μm, especially between about 50 and 500 μm. The thickness of thepolyester layer (total) is generally between about 20 and 950 μm,preferably between 50 and 300 μ. The thickness of the EVOH layer isgenerally between about 5 and 100 μm, preferably between 10 and 70 μm.The thickness of the binder layer (total) is generally between about 3and 30 μm, preferably below 10 μm. The ratio thickness of polyester(total) to thickness of EVOH can vary within broad limits; generally,this ratio is above 1, preferably above 5. The resulting bistretchedfilm shows a thickness generally between about 5 and 200 μm, especiallybetween about 10 and 100 μm. Each layer, polyester, EVOH, binder ispresent according to relative thicknesses as given above with respect tothe raw film. For example, the EVOH layer may have a thickness between 1and 10 μm.

The instant film formed of the various layers can be of variousstructures and the polyester used can vary from one layer to another.For example, one layer can be obtained from starting products containingscrap material, allowing recycling. Content of scrap is variable withinbroad limits known to the skilled man. Also, the polyester can have adifferent nature from one layer to another, or they can be the same. Allpolyester layers can be comprised of crystalline polyester, or all layercan be comprised of amorphous copolyester, or one layer can becrystalline and the other(s) can be amorphous. For example, theinvention provides 5-layer films where one layer is crystalline (i.e.PET) while the other layer is amorphous (i.e. copolyester) This allowsto combine specific mechanical properties of crystalline polyester andadhesive properties of the copolyester. It can also be forseen that eachlayer may be formed of two or more sub-layers; e.g. the outer polyesterlayer can be formed of one sub-layer of PET and one sub-layer ofcopolyester, the first one being in contact with the binder layer. Theinstant films can be used as individual layers in further multilayerfilms.

The following examples further illustrate the present invention, but donot limit the scope thereof.

EXAMPLES

EVOH:

EVOH polymer was delivered by Kuraray Eval Europe GmbH Duesseldorf.

Grade E105U, 44 mol % ethylene content, density 1.14 g/cm³, melt flowindex 5.5 g/10 min., melt point 165° C.

BINDER (Bynel)

The binder is an anhydride-modified ethylene vinyl acetate copolymer.

Density 0.95 g/cm³, melt index 10.9 g/lomin, melt point 165° C.

PET:

IV: 0.56 dl/g, melt point 256° C.

The polyester polymer was extruded at a temperature of 280° C., thebinder polymer at 240° C. The EVOH barrier polymer was extruded atdifferent temperatures (230° C., 205° C. and 175° C.). Die temperaturewas at 290° C.

The cast film samples are summarised in table 1. The thickness of thedifferent layers was confirmed via microtome-cuts under the microscope.

TABLE 1 Cast film samples EVOH PET Bynel EVOH Bynel PET Extr. Temp.Sample μm μm μm μm μm ° C. A 50 <10 50 <10 50 230 B 55 <10 40 <10 55 230C 60 <10 30 <10 60 230 D 65 <10 20 <10 65 230 E 70 <10 10 <10 70 230 F70 <10 10 <10 70 205 G 70 <10 10 <10 70 175

The cast films were cut into pieces of 11.2 cm×11.2 cm, preheated at80-90° C. for 10 sec and simultaneously stretched at 90° C. at a stretchratio of 3.3×3.3 in 2.2 sec.

The stretched samples were chucked into a frame for preheating at 170°C., 200° C. and 230° C. for 3, 8, 15 and 20 seconds. The resultingstretched films are summarised in table 2.

TABLE 2 Simultaneously stretched films Preheat Strech Heatset HeatsetRoll Temp. Temp. Stretch Temp. Time No. [° C.] [° C.] Ratio [° C.] [sec]1 80 90 3.3 × 3.3 230 20 2 80 90 3.3 × 3.3 230 20 3 80 90 3.3 × 3.3 23015 4 80 90 3.3 × 3.3 230 15 5 80 90 3.3 × 3.3 230 8 6 80 90 3.3 × 3.3230 e 7 80 90 3.3 × 3.3 230 3 8 80 90 3.3 × 3.3 230 3 9 80 90 3.3 × 3.3200 20 10 80 90 3.3 × 3.3 200 20 11 80 90 3.3 × 3.3 200 15 12 80 90 3.3× 3.3 200 15 13 80 90 3.3 × 3.3 200 8 14 80 90 3.3 × 3.3 200 8 15 80 903.3 × 3.3 200 3 16 80 90 3.3 × 3.3 200 3 17 80 90 3.3 × 3.3 170 20 18 8090 3.3 × 3.3 170 20 19 80 90 3.3 × 3.3 170 15 20 80 90 3.3 × 3.3 170 1521 80 90 3.3 × 3.3 170 8 22 80 90 3.3 × 3.3 170 8 23 80 90 3.3 × 3.3 1703 24 80 90 3.3 × 3.3 170 3

This is stretch and heatset pattern was applied for film samples D, E, Fand G.

To evaluate the influence of the thickness of the EVOH layer on theoxygen barrier, samples A-G were stretched under the same conditions(see above) and heatset at 200° C. for 8 sec.

The oxygen barrier was determined with an Ox-tran twin tester. Thefollowing table 2 provides the results.

TABLE 3 Oxygen barrier of the film samples Film EVOH EVOH OxygenThickness Thickness Extrusion Barrier Sample [μm] [μm] Temp. cc/m²/d A15 5 230° C. 5.1 B 14 4 230° C. 7.5 C 15 3 230° C. 10.2 D 14 2 230° C.13.3 E 14 1 230° C. 21.6 F 13 1 205° C. 6.6 G 13 1 175° C. 7.3

As expected, the oxygen permeability in increasing from 5 to 21 cc/m²/dwith the decreasing thickness of the EVOH barrier layer from 5 to 1 μm.But also the extrusion temperature of the EVOH polymer has a stronginfluence on the oxygen barrier. By decreasing the extrusion temperaturefrom 230° C. 205° C. the oxygen permeability drops from 21 to 6.6cc/m²/d. According to these results, a 5 μm EVOH layer extruded at 230°C. to offers the same oxygen barrier than a 1 μm EVOH layer extruded at205° C.

Samples D-G were examined more intensively regarding the influence ofheatset time and temperature. The results of the oxygen barrier aresummarised in table 4.

TABLE 4 Oxygen barrier (expressed in cc/m²/d) for samples D- G atdifferent heatset conditions (see table 2) Roll N° Sample D Sample ESample F Sample G 1 15.1 25.7 6.2 9.3 3 17.5 26.3 5.3 9.2 5 14.1 27.46.6 7.8 7 16.6 28.0 nd 8.9 9 16.2 25.6 5.9 9.5 11 17.0 26.8 5.7 10.0 1314.5 27.4 5.7 8.2 15 15.0 24.5 5.5 8.9 17 18.1 25.7 6.3 8.5 19 20.5 28.45.9 7.2 21 16.5 21.6 5.7 7.2 23 14.5 23.2 7.3 8.5 nd: not determined

Like in table 3, the oxygen permeability is increasing with decreasingEVOH layer thickness and decreasing with lower EVOH extrusiontemperature.

However, it can be said that there is no dependence of the oxygenbarrier on heatset time and temperature. High oxygen barrier propertiesmay however be obtained with a lower EVOH extrusion temperature, such asabout 205° C.

Mechanical properties, i.e. modulus, tensile strength, force at 3%elongation (F3), force at 5% elongation (F5) and elongation at break,along the MD (machine direction) and the TD (transverse direction) weredetermined with an Instron equipment at room temperature.

For samples A-G, the mechanical properties at heatset conditions of 200°C. and during 8 sec, are listed on the following table 5.

For samples D-G, the mechanical properties at all heatset conditions(see table 3), are listed on the following pages on table 6-9.

TABLE 5 Mechanical properties of samples A-G Modulus [N/mm²] F3 [N/mm²]F5 [N/mm²] Tensile [N/mm²] Elongation [%] Sample MD TD MD TD MD TD MD TDMD TD A 3610 3563 83 81 97 95 174 166 111 116 (15 μm) B 3768 3770 87 86101 100 182 181 105 117 (14 μm) C 3934 3783 90 86 105 102 204 203 110130 (15 μm) D 3862 3731 90 86 105 103 205 190 113 122 (14 μm) E 40323809 92 89 109 105 201 209 97 131 (15 μm) F 3690 3620 84 83 96 95 162150 112 96 (13 μm) G 3741 3726 85 85 98 99 170 154 94 84 (13 μm)

TABLE 6 Mechanical Property Data Sample D (Thickness = 14 μm) ModulusModulus F3 F3 F5 F5 Tensile Tensile Elongation Elongation MD TD MD TD MDTD MD TD MD TD Roll N^(o) [N/mm²] [N/mm²] [N/mm²] [N/mm²] [N/mm²][N/mm²] [N/mm²] [N/mm²] [%] [%] 1 3981 4140 87 87 93 93 172 173 127 1163 4005 4064 87 88 95 97 181 184 117 114 5 4099 4229 87 87 95 94 183 177109 114 7 4099 4363 86 92 95 101 181 194 106 106 9 3896 4025 86 88 97 97190 188 106 122 11 3935 3986 85 85 93 93 179 172 110 109 13 4116 4276 8889 96 97 200 173 121 101 15 4120 4208 89 89 98 98 195 192 111 114 174158 3849 89 85 100 95 200 201 110 126 19 4145 4156 89 88 100 99 203 203114 118 21 4051 4074 88 89 98 99 219 208 126 114 23 3967 4251 87 93 96103 212 227 121 118

TABLE 7 Mechanical Property Data Sample E (Thickness = 14 μm) ModulusModulus F3 F3 F5 F5 Tensile Tensile Elongation Elongation MD TD MD TD MDTD MD TD MD TD Roll N^(o) [N/mm²] [N/mm²] [N/mm²] [N/mm²] [N/mm²][N/mm²] [N/mm²] [N/mm²] [%] [%] 1 4541 4770 92 91 99 103 179 193 106 1043 4316 4497 92 94 102 103 201 207 118 110 5 4655 4712 97 96 104 104 200209 107 112 7 4488 4508 94 94 102 102 183 198 86 107 9 4528 4420 95 94104 103 207 208 113 116 11 4307 4393 91 92 100 103 198 208 106 121 134421 4344 92 91 101 99 202 192 121 116 15 4173 4521 89 94 98 104 205 209129 111 17 4316 4357 94 94 105 107 212 229 116 116 19 4186 4269 91 92101 103 206 196 116 116 21 4136 4023 87 89 97 100 197 213 102 120 234171 4082 92 90 102 100 207 203 115 119

TABLE 8 Mechanical Property Data Sample E (Thickness = 13 μm) ModulusModulus F3 F3 F5 F5 Tensile Tensile Elongation Elongation MD TD MD TD MDTD MD TD MD TD Roll N^(o) [N/mm²] [N/mm²] [N/mm²] [N/mm²] [N/mm²][N/mm²] [N/mm²] [N/mm²] [%] [%] 1 3416 3688 73 77 78 82 139 155 113 1183 3742 3388 78 73 82 76 143 133 109 124 5 3603 3334 75 73 78 77 143 123109 116 7 3211 3516 71 75 75 79 118 130 98 76 9 3247 3580 71 77 77 83142 145 103 106 11 3577 3476 77 74 83 80 148 135 99 88 13 3199 3608 7177 76 83 140 147 118 91 15 3216 3590 71 77 76 84 140 141 111 82 17 37993729 78 84 78 86 193 190 113 107 19 3745 3619 79 82 85 82 183 183 107117 21 3655 3609 77 76 83 82 188 178 107 95 23 3436 3294 75 72 82 77 151144 102 125

TABLE 9 Mechanical Property Data Sample E (Thickness = 13 μm) ModulusModulus F3 F3 F5 F5 Tensile Tensile Elongation Elongation MD TD MD TD MDTD MD TD MD TD Roll N^(o) [N/mm²] [N/mm²] [N/mm²] [N/mm²] [N/mm²][N/mm²] [N/mm²] [N/mm²] [%] [%] 1 3818 3971 82 85 89 92 163 173 123 1193 3996 3868 84 83 91 89 165 159 113 107 5 3891 3853 82 82 88 88 163 157109 105 7 3710 4008 81 84 87 82 159 162 115 87 9 3614 3926 80 84 87 93154 168 105 93 11 3577 3845 80 84 88 92 154 167 106 107 13 3653 3748 8082 88 89 162 155 118 105 15 3674 3803 80 82 88 89 151 161 99 97 17 38983831 83 81 91 89 205 186 120 100 19 3560 3530 79 78 87 85 155 157 107120 21 3677 3677 79 79 86 86 187 194 122 133 23 3425 3536 76 79 82 85153 153 115 103

From the above results, it can be concluded, that a heatset time between3 and 8 seconds is best suited to obtain a stabilised polyester barrierfilm with useful mechanical properties and a high oxygen barrier.

It can also be concluded that the invention allows processing of EVOHcopolymer with high ethylene content while still obtaining very goodbarried (oxygen barrier) properties; this is surprising since it isgenerally admitted that high ethylene content and high barrier propertyare antinomic.

The invention was described with reference to a preferred embodiment.However, many variations are possible within the scope of the invention.

What is claimed is:
 1. A process for manufacturing a multilayer film,comprising at least a layer of EVOH, a layer of a coextrusion binder,and a layer of polyester, comprising the steps of: (i) coextruding alayer of EVOH, a layer of a coextrusion binder and layer of polyester;(ii) simultaneously bistretching the layers of (i); and (iii) heattreating the layers of (ii) at a temperature between 170° C. and 250° C.and during a heat treatment time below 8 sec.
 2. The process accordingto claim 1, where the heat treatment time is comprised between 3 andbelow 8 sec.
 3. The process according to claim 1 where the heattreatment temperature is below 220° C.
 4. The process according to claim1 where the heat treatment temperature is between 180 and 210° C.
 5. Theprocess according to claim 1 where a ratio thickness of polyester tothickness of EVOH is above
 5. 6. The process according to claim 1 wherethe EVOH extrusion temperature is below 220° C.
 7. The process accordingto claim 1 where the simultaneously bistretching is performed at atemperature between 75 and 130° C.
 8. The process according to claim 1where the simultaneously bistretching is performed at stretching ratiosof from 2 to 5 in each direction.
 9. The process according to claim 1with preheating before the bistretching step (ii).
 10. The processaccording to claim 1 where the multilayer film is a 5-layer filmpolyester/binder/EVOH/binder/polyester.
 11. The process according toclaim 1 where the EVOH contains more than 30 mol % of ethylene.
 12. Theprocess according to claim 1 where the polyester is PET.
 13. The processaccording to claim 1 where the binder is an anhydride-modified ethylenevinyl acetate copolymer.